DE 42 04 386 C2 discloses a system separator having a housing, the housing of which defines an inlet chamber, an intermediate chamber and an outlet chamber, wherein the system separator furthermore has two backflow preventers positioned in the housing and arranged in series in the through flow direction of a medium, namely a first, inlet-side backflow preventer, arranged between the inlet chamber and the intermediate chamber, and a second, outlet-side backflow preventer, arranged between the intermediate chamber and the outlet chamber. The system separator disclosed there furthermore comprises a discharge valve, by means of which the intermediate chamber between the two backflow preventers can vent or be emptied, wherein the discharge valve is controlled in accordance with a differential pressure between the pressure in the inlet chamber and the pressure in the intermediate chamber. The discharge valve opens to connect the intermediate chamber to the atmosphere for air admission when this differential pressure falls below a defined limit value.
DE 20 2005 020 081 U1 discloses another system separator having an inlet-side backflow preventer arranged between an inlet chamber and an intermediate chamber, an outlet-side backflow preventer arranged between the intermediate chamber and an outlet chamber, and a discharge valve, wherein, according to this prior art, the housing of the system separator is designed as a two-part housing, which comprises a first, upper housing part and a second, lower housing part.
Via the first housing part, the system separator in DE 20 2005 020 081 U1 can be connected to a first line, in particular to a standpipe, or to an upstream pressure zone. The second housing part accommodates the two backflow preventers and serves to connect the system separator to a second line or to a downstream pressure zone. According to this prior art, the two housing parts of the housing of the system separator are screwed to one another, for which purpose the first, upper housing part has a section with an external thread and the second, lower housing part has a section with an internal thread, which engage in one another when screwed together.
Another system separator is known from DE 20 2009 016 823 U1, wherein a one-piece housing is provided in this system separator, and wherein the inlet chamber of the system separator is assigned a shutoff valve, by means of which the inlet chamber can be separated from an upstream pressure zone.
DE 20 2014 001 685 U1 discloses another system separator having a housing, wherein once again two backflow preventers and a shutoff valve are accommodated in the housing. It is furthermore already known from this prior art that a pressure reducer can be integrated into the housing upstream of the two backflow preventers, this pressure reducer then being arranged between an inlet-side connection stub of the housing and the inlet chamber of the inlet-side backflow preventer. The pressure reducer limits the pressure prevailing in the inlet chamber to a pressure level below the pressure at the inlet-side connection stub of the system separator.
In practice, it has been found that, when a pressure reducer is integrated into the system separator upstream of the two backflow preventers and when the pressure prevailing at the inlet stub falls below the pressure in the inlet chamber, the pressure reducer does not open and thus the pressure in the inlet chamber remains constant.
In this case, it is then not possible to empty the system separator by opening the discharge valve in the region of its intermediate chamber since, despite the fall in the pressure difference, decisive for this purpose, between the pressure at the inlet-side connection stub and the pressure in the intermediate chamber, the pressure difference between the inlet chamber and the intermediate chamber does not fall in a corresponding fashion.